One type of packing machines uses plastic film to wrap products so as to prevent the products from being contaminated, the plastic film originally provided in the machine is in the form of a roll of plastic film which is unwrapped by motors and rollers. An outer diameter of the plastic film roll will be gradually reduced because the plastic film is unwrapped from the plastic film roll continuously so that a tension force of the plastic film unwrapped from the plastic film roll varies as the outer diameter of the plastic film roll reduces, and this results in fluctuant wrapping results. In order to resolve the problem, an additional tension adjusting mechanism is added to the packing machine so as to control the tension force on the unwrapped plastic film. By operating the tension adjusting mechanism, the tension force on the plastic film can be maintained at a constant value. However, the additional tension adjusting mechanism occupies a large space so that the packing machine has a larger volume and becomes a complicated structure which is expensive. Furthermore, the complicated structure means higher maintenance costs are required.
The present invention provides a tension adjusting device for a packing machine using plastic film and is able to automatically adjust the tension force on the plastic film during the packing process so that the disadvantages of the conventional tension adjusting mechanism of the packing machine can be mitigated and/or obviated.